Escherichia coli, or E. coli, bacteria (National Institute of Allergy and Infectious Diseases)
27 June 2019. Genetically-altered E. coli bacteria can act as sensors for certain chemicals, when installed on a programmable robotic arm and gripper. Engineering researchers at University of California in Davis and Carnegie Mellon University in Pittsburgh describe their system and proof-of-concept test results in yesterday’s issue of the journal Science Robotics (paid subscription required).
A team led by biomedical engineering professor Cheemeng Tang at UC-Davis and Carnegie Mellon mechanical engineering professor Carmel Majidi is aiming to improve the ability of robots to sense chemical signals in their immediate environment. Achieving this task, say the authors, requires biologically-based sensors that react in the presence of target chemicals, as well as components that convert the signals to electronic data on which other robotic system modules can act.
Tang’s lab at UC-Davis studies synthetic biological systems, including artificial cells and genetically-engineered organisms mainly for protein design, drug discovery, and treatments for disease. At Carnegie Mellon, Majidi’s group investigates so-called soft materials that help make robotic systems safer for interacting with humans, including fabrication methods to produce those materials.
Tang, Majidi, and colleagues first created sensors with engineered E. coli bacteria to react in the presence of IPTG, short for isopropyl-beta-D-thiogalactoside, a commercially-available chemical used in lab cloning experiments. E. coli, or Escherichia coli, is best known as a bacteria causing intestinal infections, although most strains of E. coli are harmless. Because E. coli is a well-studied bacteria, it is often used as a model organism in labs. In this case, the researchers engineered a form of E. coli to express fluorescing proteins that illuminate in the presence of IPTG. The engineered E. coli are stored and sealed in 3-D printed plastic wells, yet thin enough to allow IPTG signals to permeate.
The researchers then designed a device to convert light from the altered E. coli into electronic data. For this task, the team uses a circuit with a light-emitting diode or LED that detects light given off by the engineered bacteria, and photo-transistor to convert the detected light into electronic signals. The circuit is printed on soft, flexible materials that can fit on the end of a robotic arm and gripper. Electronic data from the circuit are used to control the actions of a pneumatic network, or pneu-net, actuator that bends the gripper device in the desired direction.
The team tested their system with a hydrogel, a water-based polymer, infused with IPTG and released in a water bath. Sensors on the gripper reacted to the presence of IPTG and reported illumination intensities 300 times greater than a comparison fluid without IPTG. The researchers then devised an exercise, where the robotic gripper is programmed to pick-up and move a plastic ball into a liquid bath, only if the bath tests negative for IPTG. The results, as seen in this video hosted by EurekAlert, show the gripper accurately responds to the presence of IPTG in the solution, and deposits the object in the bath only when IPTG is absent.
The researchers recognize their system is designed to detect only one chemical, and challenges remain in detecting specific concentrations and maintaining stable concentrations of microbes in a robotic device. Nonetheless, says Majidi in a UC-Davis statement, “we are closer to future breakthroughs like soft bio-hybrid robots that can adapt their abilities to sense, feel and move in response to changes in their environmental conditions.”
Carnegie Mellon filed patent applications for some of the technologies in the paper.
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- Electronic Skins Add Robotic Functions to Objects
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